Aspects of this disclosure relate generally to telecommunications, and more particularly to special subframe configuration in unlicensed spectrum communications.
Wireless communication systems are widely deployed to provide various types of communication content, such as voice, data, multimedia, and so on. Typical wireless communication systems are multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, and others. These systems are often deployed in conformity with specifications such as Third Generation Partnership Project (3GPP), 3GPP Long Term Evolution (LTE), Ultra Mobile Broadband (UMB), Evolution Data Optimized (EV-DO), Institute of Electrical and Electronics Engineers (IEEE), etc.
In cellular networks, “macro cell” base stations provide connectivity and coverage to a large number of users over a certain geographical area. A macro network deployment is carefully planned, designed, and implemented to offer good coverage over the geographical region. Even such careful planning, however, cannot fully accommodate channel characteristics such as fading, multipath, shadowing, etc., especially in indoor environments. Indoor users therefore often face coverage issues (e.g., call outages and quality degradation) resulting in poor user experience.
To improve indoor or other specific geographic coverage, such as for residential homes and office buildings, additional “small cell,” typically low-power base stations have recently begun to be deployed to supplement conventional macro networks. Small cell base stations may also provide incremental capacity growth, richer user experience, and so on.
Recently, small cell LTE operations, for example, have been extended into the unlicensed frequency spectrum such as the Unlicensed National Information Infrastructure (U-NII) band used by Wireless Local Area Network (WLAN) technologies. This extension of small cell LTE operation is designed to increase spectral efficiency and hence capacity of the LTE system. However, it may also encroach on the operations of other Radio Access Technologies (RATs) that typically utilize the same unlicensed bands, most notably IEEE 802.11x WLAN technologies generally referred to as “Wi-Fi.”
Further, the massive growth in data traffic on both mobile and wireline networks and the proliferation of smart phones and other connected devices continue to put pressure on network operators to increase capacity. For mobile network operators, spectrum is a fundamental resource in this pursuit. However, the licensed spectrum, especially the valuable low-frequency bands with low propagation loss traits, is limited, and is rapidly being exhausted by a dense and growing subscriber base. With a significant amount of unlicensed spectrum globally available in the 5 GHz band (and other bands), the mobile operators and vendors are looking to use unlicensed spectrum to augment the capacity of licensed frequency carriers. As such, LTE in unlicensed spectrum, sometimes referred to as LTE over unlicensed spectrum or simply LTE-U, is proposed to utilize unlicensed spectrum to carry data traffic for mobile services with the initial focus on the 5725-5850 MHz band for this use.
In LTE in unlicensed spectrum, a load-based equipment (LBE) may be configured to perform an extended clear channel assessment (ECCA) check in which the operating channel that corresponds to the unlicensed spectrum is observed for a duration. As such, the LBE may determine that the operating channel is clear for transmitting data after the operating channel is silent for at least the duration. As referenced herein, an LBE may refer to an equipment where the transmit/receive structure is not fixed in time but determined by communication demand. Further, aligning the duration across cells of a same operator may help aligning idle time/transmission time among different cells or user equipment (UE) and help increase frequency reuse within the same operator.